If you remove ground from the adams (sub and speakers) it might be fixed. If yes you know it is a ground loop between the computers power supply and the speakers. PSU's can cause lots of noise on the ground line.
This is not a permanent solution, only for a quick test. Permanent  would be disconnecting pin 1 from the XLR.

Also if you disconnect the RME and Adams and use phones you will know if the output from the RME is clean.

If you are good with a soldering iron, disconnecting pin 1 in the XLR is 100% safe.
Also since there is a ground loop, disconnecting earth from the sub for a few seconds will not make it ungrounded (since it is connected through the loop) and will tell you 100% sure what the issue is. If you try this also disconnect the speakers from the sub since that is another possible ground loop.

Agreed and MC has said the same. Firewire has that risc build in by how its pins can connect in the wrong order and yes I blew up an expensive firewire card in on of my audio interfaces (Tascam FW1804)

Maybe not completely.

Just plugging the power plugs into the same power strip usually does not help.

As mentioned:
All interconnect lines, even power, have to be routed into one strand, as close together as possible.
Think of it as one solid tree, possibly with branches (to the monitors), but no connections in between.

This sounds to be contrary to what's usually said: separate power and audio cables.
But, if the audio cables are well screened and signals are high, line level, this approach does not have any disadvantages and does always work.

For further reduction in hum (and noise) you can dial down the inputs on your ADAM monitors (if possible) and drive them hotter from the ADI-2.
If the monitors do not have an input level control or not enough down range there, you can use pads to reduce their sensitivity, look here:
https://forum.rme-audio.de/viewtopic.php?id=25399

This even makes better use of ADI-2's level capabilities.

PS:  I just had a look at the ADAM homepage.
There are no usable level controls, so (switchable) level pads are the best option.
You would place them at the input of the sub.

Not necessary - this solution is taxing the common mode rejection of a balanced input.

And breaking an interface chip is again easily possible.

If you go that route, coupling the screen via a 10nF ceramic capacitor paralleled with a 100 Ohms resitor, takes this load from the following input stage - and discharges voltages that can break a chip.

Just removing the cable screen from XLR pin 1 can have lot's of adverse effects, from sound degradation to broken electronics on both sides of the connection.

Connecting the screen to XLR pin 1 through a parallel arrangement of 10nF capacitor and 100 Ohms resistor maintains the ground reference function of the screen, while breaking the existing ground loop.

Usually it's better to do this on the sender side, XLR female.
This way the screen does it's job for the balanced receiver.
And - there's more space in the female plug on some (with Neutrik both are the same).

Parallel means side by side, not one after the other - sometimes missunderstood.

The values of C and R are kind of prooven, but not need to be maintained exactly.